Present dietetic needs, predilections, and perceptions have led to the increased use of replacement sweeteners as a substitute for the "natural" sugars, including sucrose and fructose. Although such replacement sweeteners are under continual review for their long term physiological affects, their demand has grown unabated. Accompanying their growth as a commercial product area with substantial economic impact has been a renewed emphasis on discovering and supplying new replacement sweeteners.
Among its characteristics, the ideal replacement sweetener would be noncaloric, noncariogenic, without detrimental physiological effects, and usable by diabetics. These requirements would be met if a sweetener were not metabolized by humans and by flora which are found in the mouth and intestinal tract, and if it were without effect on any internal organ. The ideal sweetener should be excreted in the same form as when ingested. Another desirable feature is that it have bulking properties similar to sucrose and browning ability so that it can be substituted for table sugar (sucrose) and dextrose in many formulations.
Recently, attention turned toward the L-sugars as desirable replacement sweeteners. It has been known since at least 1946 that L-fructose is sweet (M. L. Wolfrom and A. Thompson, J. Am. Chem. Soc., 68, 791,793 (1946)), and since at least 1890 that L-fructose is nonfermentable (E. Fischer, Ber. Deutsch. Chem. Ges., 23, 370,389 (1890)), hence not metabolized by microorganisms generally metabolizing D-sugars. A reasonable, although not necessarily correct, inference is that it also is not metabolized by humans. Unfortunately, the early hopes and expectations raised for L-hexoses were not corroborated by experimental observations, leading ultimately to a search for other "ideal" sweeteners.
Even though one might have expected the sweetness of the D-hexose monosaccharides to have been thoroughly investigated previously, this is not the case. Among the aldol hexoses D-glucose is of course widely known to be sweet, and D-gulose is reported to be a sweet syrup (Merck Index, 10th Edition, page 659 (4458)). More recently D-galactose has been found to be sweet (Shallenberger and coworkers, Nature, 221, 555 (1969)). Although mannose also is reported to be sweet, the situation is somewhat complicated by the; fact that its two enantiomers appear to have distinctly different organoleptic properties, with .beta.-D-mannose actually being bitter: G. G. Birch and coworkers, J. Sci. Fd. Agric., 21, 650 (1970); R. S. Shallenberger and coworkers, J. Food Sci., 30, 560 (1965); "Sugar Chemistry", R. S. Shallenberger and G. G. Birch, page 117, The AVI Publishing Company, Inc., (1975). It should be apparent that a bitter taste is an objectionable organoleptic property in a substance contemplated for use in foods as a sweetener or sweetener replacement. Of the ketohexoses the sweet taste of D-fructose is common knowledge, and more recently D-tagatose has been reported to be sweet. See U.S. Pat. No. 4,786,722 and references cited therein.
The metabolism of D-glucose and, to a lesser extent D-galactose, is relatively well studied, but reports on other D-aldohexoses are sparse. Fischer and Thieffelder, op. cit. reported that D-mannose was readily fermented by most, but not all, yeasts they were tested against, but that D-talose was not fermented by any of the twelve. Of the D-ketohexoses the metabolic fate of D-fructose is well documented. Recently the patentee in U.S. Pat. No. 4,786,722 reported that most of D-tagatose given orally to rats was recovered in the feces. However, the lack of detailed experimental data make the qualitative statement of results difficult to evaluate.
Recently the patentees of U.S. Pat. No. 4,963,382 found that both D-talose and D-allose are sweet, that neither has any strong objectionable taste characteristics, and that neither is substantially metabolized in rats. There also are strong indications that at least D- allose is non-cariogenic. Our findings make possible a means to provide reduced calorie sweetening to foods while mimicking other effects of sucrose in foodstuffs, effects to which society has become accustomed through the ages. Thus it appears that D-allose in particular may serve as a reduced-calorie bulking sweetener which can be substituted for sucrose and dextrose in a wide variety of food formulations without necessitating any large changes in recipes, which can be expected to be metabolized in humans to only a small extent, if at all, which undergoes a browning reaction when heated or baked, and which is readily crystallized. Crystallinity often is needed to impart the correct mouth feel to a given foodstuff.
D-allose also holds interest as a component of new pharmaceuticals, especially antiviral agents where one component may be an aldohexose or a derivative thereof. Consequently there is a need for preparing high purity D-allose in quantities not previously possible.